The present invention relates, in general, to the field of mold clamping units.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
German Pat. No. 101 61 911 C1 describes a mold clamping unit having a movable platen which is adjustably connected by means of a spindle nut to tie bars, constructed in an adjustment zone as threaded spindle, for adapting the mold installation height to particular requirements. A switching mechanism in the form of a hydraulic servomotor acts between the movable platen and the spindle nut in order to clear in release position the axial play between the spindle nut and the movable platen so as to enable the spindle nut to rotate, and to brace the spindle nut in active state free of play and non-rotatably on the platen to thereby lock the adjusted mold installation height upon the threaded connection. Such an adjustment system for adapting the mold installation height has shortcomings because the play between spindle nut and tie bar cannot be eliminated. As a result, the thread flanks encounter sudden load changes, when the movable platen reverses direction, causing annoying noise development and especially requiring a hydraulic servomotor that must be constructed powerful enough to be able to withstand the stress experienced during aplication of the high clamping forces and the much higher locking forces between the movable platen and the tie bar.
German Pat. No. 102 10 869 C1 describes a mold clamping unit having a support platen which is rigidly connected with a fixed platen via tie bars and threadably connected via a spindle nut for lengthwise displacement with the tie bar end portions for realizing a mold height adjustment. The spindle nut is locked by a counternut which is threadably connected to the tie bars and braced with the spindle nut by resilient elements acting between the counternut and the support platen. A switch to the release position is effected by the stroke drive which moves the movable platen beyond the normal opening position so that the spindle nut and the counternut are no longer clamped to one another and the spindle nut can be turned by a rotary drive to a new mold installation height. As a consequence, essential components of the clamping unit, in particular the stroke drive applying the locking force must be oversized and the length of the tie bars must be configured longer to account for the required added stroke travel to release the mold height adjustment.
It would therefore be desirable and advantageous to provide an improved mold clamping unit which obviates prior art shortcomings and which is simple and compact in construction to attain a reliable release and play-free locking of the mold height adjustment, without experiencing any downtimes in operation of the mold clamping unit.